During various well drilling operations, it is desirable to close off the upper end of a well casing from downhole pressures, such as when it is desirable to effect repairs to or modifications of the tree at the top of the well casing.
While there are various tools which may accomplish the desired function, most of these are placed within the well casing through the utilization of a wire line and are not only sometimes difficult to properly install but also sometimes impossible to remove as desired requiring that their removal be effected by fishing or milling operations. Accordingly, a need exists for a means by which downhole pressure may be controlled in an effective manner through the utilization of an apparatus which may be readily inserted downwardly in the casing and removed therefrom whenever desired.